1. Field of the Invention
The present invention relates to a keyboard of a membrane contact type for use as an input keyboard for electronic equipments such as computers, data processors and word processors.
2. Description of the Prior Art
Japanese Utility Model Laid-Open Publication Nos. 56-165328 and 59-170922 disclose inventions relating to such a keyboard of a membrane contact type.
A membrane contact sheet employed in a conventional keyboard of a membrane contact type, has a flexible insulating membranous substrate having a movable section and a fixed section demarcated by folding along a folding line provided at the center of the substrate.
The movable section has a plurality of movable contacts. The number of the movable contacts is equal to that of keys and the arrangement of the movable contacts corresponds to that of the keys. Each movable contact is moved upon reception of a pressure applied to each key corresponding to the each movable contact. The fixed section has a plurality of fixed contacts. The arrangement of the movable contacts and that of the fixed contacts are symmetrically arranged with each other with respect to the folding line.
A plurality of the movable contacts are divided into a plurality of lateral lines and the movable contacts on each lateral line are connected in series by a wiring line, while a plurality of the fixed contacts are divided into a plurality of longitudinal rows and the fixed contacts on each longitudinal row are connected in series by a wiring line to form a matrix of contacts. The wiring lines lead respectively to terminal sections.
The membrane contact sheet is folded along the folding line so that the printed surfaces of the movable section and the fixed section face each other, an insulating spacer having openings formed at positions respectively corresponding to the contacts is placed between the movable section and the fixed section, and then the movable section and the fixed section are joined adhesively to form a membrane contact unit.
The conventional membrane contact sheet, however, has a disadvantage that a wiring pattern including those wiring lines needs inevitably to be formed via a long way around the arrangement of the fixed contacts to lead the wiring lines of the movable contacts to the terminal section, and thereby the size of the keyboard and the resistances of the wiring lines are increased.
Such a disadvantage may be overcome by providing the terminal section of the movable contacts on the movable section. This is realized by printing patterns of contacts and the wiring lines on both major surfaces of a membrane contact sheet or by employing a printed wiring board having printed wiring patterns on both sizes thereof. However, such means is unable to simplify the morphology of the membrane contact unit and to reduce the component parts.